The present invention relates to a new and improved construction of a method of, and apparatus for, continuously casting rapidly solidifying material.
In its more particular aspects, the present invention specifically relates to a new and improved method of, and apparatus for, continuously casting rapidly solidifying material and which method and apparatus uses a slot-like nozzle through which the hot liquid material flows to a cooled surface or wall which is moved past the slot-like nozzle at a close spacing. The movable cooled surface or wall is made of a material having high heat conductivity. The material cast onto the movable cooled surface or wall solidifies on such surface or wall and is detached from the movable cooled surface or wall after movement through a predetermined distance.
Such apparatus as known, for example, from U.S. Pat. No. 4,142,571, granted March 6, 1979, and European Pat. No. 2,785 makes use of a process known, for example, from the technical journal "Zeitschrift fur Metallkunde", Vol. 64, pgs. 835 to 843, 1973, under the designation "Melt Spin Process". This process, in turn, is based on ideas which have originated from Sir Henry Bessemer, E. H. Strange and C. A. Pim.
Such a process is particularly suitable for manufacturing foils of metals or alloys, optionally with the addition of fine non-metallic particles. Such foils possess an extremely fine-grain or amorphous, glass-like structure which cannot be obtained using conventional casting processes. In order to obtain this structure and the novel material properties associated therewith, it is necessary for the melt to extremely rapidly solidify on the moving cold or cooled surface or wall, i.e. at an extremely high cooling rate of at least 10.sup.4, preferably approximately 10.sup.6 .degree. C./sec, before the solidified foil is detached from the cooled surface or wall by means of a suitable detaching device or under the action of a centrifugal force and is then passed on for further use or processing.
Due to the high heat input into the moving cooled surface or wall, the first known melt spin apparatuses were heat capacity of the moving cooled surface or wall was only suitable for discontinuous operation during which the sufficient to absorb the amount of heat of a produced charge. In order that the delivered heat may be absorbed quite well, the moving cooled surface or wall is made of a highly heat-conductive material, preferably copper or an alloy such as beryllium/copper.
In order to maintain a continuous operation, it would be necessary to cool the moving surface or wall in the most effective manner possible. However, only a small amount of heat can be removed in the case of cooling by means of gas flows which are blown onto the wall surface. Cooling by means of water or other liquids on the wall surface at which the melt solidifies, easily leads to contamination of the wall surface. Such contamination impedes or even renders impossible the casting operation. In addition, adjustability or variability of the cooling across the width of the moving surface or cooled wall neither was possible nor recognized as being desirable.
A further problem which results during the production of particularly wide foils, is associated with the thickness constancy of the produced foils. Experience has shown that already in the case of comparatively narrow foils, there is a tendency towards thickening of the edges or rim portions. It has been attempted in known apparatuses to achieve uniform thickness by maintaining specific gap or nozzle gap dimensions and gap or nozzle gap spacings from the moving cooled surface or wall. However, using such arrangement, there could not be achieved any possibility of correcting foil thickness deviations and maintaining predetermined desired thickness values during a continuously operating process.
European Pat. No. 8,901 which is cognate to U.S. Pat. No. 4,193,440, granted Mar. 18, 1980, and French Pat. No. 2,307,599 which is cognate to U.S. Pat. No. 4,061,178, granted Dec. 6, 1977, and U.S. Pat. No. 4,190,103, granted Feb. 26, 1970, describe strip or band casting means for low-melting metals. Therein, the melt is introduced into the gap formed between two water-cooled metal strips or bands. The two strips or bands are pressed against one another by pairs of cooling support elements only at a predetermined distance following the melt feeding location as viewed in the direction of movement. In this arrangement, however, the melt cooling rate is insufficient for forming a metal foil having an amorphous structure.
European Pat. No. 41,277 which is cognate to U.S. Pat. No. 4,434,836, granted Mar. 6, 1984, describes a casting process during which the molten metal or melt is poured into a groove formed on the inside of a metal cylinder which is cooled on the outside by means of cooling water nozzles at a predetermined distance following the feeding location. In this construction, again the cooling rate is insufficient for producing an amorphous structure. No thickness regulation is provided.
Furthermore, U.S. Pat. No. 3,712,366, granted Jan. 23, 1973, describes a metal casting process during which the molten metal or melt is solidified on the outer surface of a cylinder which is cooled by water which is uniformly propelled onto the entire inside of the cylinder under the action of centrifugal forces. The cooling rate which can be achieved in this arrangement, once again is insufficient for forming amorphous metal structures. Also in this construction no thickness regulation is provided.
In the continuous casting process described in French Pat. No. 2,347,999 which is cognate to U.S. Pat. No. 4,091,862, granted May 30, 1978, the metal melt is passed between two guide plates which are cooled on the outside using cooling support elements. Also in this construction, the solidification rate is not sufficiently high.